The present invention generally pertains to radiant energy collection systems and is particularly directed to an improvement in multi-spectral target detection systems. A multi-spectral target detection system may be used for detecting radiation in diverse portions of the electromagnetic spectrum.
Radio frequency and electro-optical radiation detection systems have been employed to detect the presence of and/or track moving and stationary targets and to measure some of their characteristics. The uses of these systems range from the detection of military targets to the spectral analysis of molten metals.
When separate detectors for detecting radiation from a single target within diverse portions of the electromagnetic spectrum are placed in a common focal plane defind by a radiant energy collection system, the separate detectors do not view the same target feature (and possibly not even the same target) at the same time unless they are axially coincident. This means that several undesirable effects can occur as the target moves or is scanned.
First, not all of the detectors may ever see the same target feature. Second, there is no prdetermined order in which the separate detectors may see a given feature of the target. Third, the separate detectors see either different features of the target or different targets altogether at any given instant. As a result of the first case, no meaningful comparison of radiant energy received by the separate detectors can occur. The second case necessitates complex signal processing for comparison purposes, which produces target misses and false alarms. The third can also results in target misses and false alarms.
If the separate detectors in the same focal plane are axially coincident, they are difficult and expensive to build and lose efficiency due to fabrication and internal absorption.